1. Field of the Invention
The present invention relates to a relay system, and more particularly to a transmitting/receiving apparatus.
2. Description of the Background Art
FIGS. 1 and 2 illustrate a transmitting apparatus 100 and a receiving apparatus 110 of a repeater system.
As shown in FIG. 1, the receiving apparatus 100 of a repeater system includes a receiving antenna 11 for receiving a weak signal propagated from a base station; a band-pass filter 12 for filtering the signal received through the receiving antenna 11; a low noise amplifier 13 for low-noise amplifying the frequency signal (S_Rx) outputted from the band-pass filter 12; and a mixer 14 for mixing the output signal of the low noise amplifier 13 and a local signal (LO) to obtain a downwardly converted intermediate frequency signal (IF_Rx).
As shown in FIG. 2, the transmitting apparatus 110 of the repeater system includes a mixer 21 for mixing the intermediate frequency (IF_Tx) outputted from the receiving apparatus 100 and a local signal (LO) to obtain an upwardly converted radio frequency (RF) signal, a power amplifier 22 for amplifying the radio frequency (RF) signal outputted from the mixer 21; a low-pass filter 23 for removing an unnecessary component from the output signal of the power amplifier 22; and a transmitting antenna 24 for transmitting the transmission signal (S_Tx) outputted from the low-pass filter 23.
The operation of the transmitting and receiving apparatuses 100 and 110 of the repeater system constructed as described above will now be explained.
Generally, a repeater system receives a weak signal through a receiving antenna from the base station, amplifies it to transmission signal with a relatively high power and transmits it through a transmitting antenna.
In detail, in the receiving apparatus of a repeater system, the receiving antenna 11 receives a weak signal propagated from the base station and provides it to the band-pass filter 12, which extracts a frequency signal (S_Rx) existing in a certain range of the received signal. The low-noise amplifier 13 low-noise amplifies the frequency signal (S_Rx) outputted from the band-pass filter 12, and the mixer 14 mixes the local signal (LO) with the output signal of the low-noise amplifier 13 to obtain the downwardly converted intermediate frequency signal (IF_Rx).
Meanwhile, in the transmitting apparatus 110 of the repeater system, the mixer 21 mixes the local signal (LO) with the intermediate frequency (IF_Tx) signal to obtain the upwardly converted radio frequency (RF) signal, and the power amplifier 22 amplifies the radio frequency signal outputted from the mixer 21. The low-pass filter 23 removes the unnecessary component from the output signal of the power amplifier 22 and provides it to the transmitting antenna 234. Then, the transmitting antenna 24 transmits the transmission signal (S_Tx) outputted from the low-pass filter 23 toward a destination.
However, as for the conventional repeater system, since the weak signal received through the receiving antenna 11 from the base station is amplified to a transmission signal with a relatively high power, when the receiving apparatus 100 of the repeater system, where the transmitting apparatus and receiving apparatus coexist, receives the next signal from the base station, the transmission signal (S_Tx) transmitted from the transmitting antenna 24 happens to be inputted to the receiving apparatus. At this time, the transmission signal (S_Tx) has a phase difference in proportion to the distance between the transmitting antenna 24 and the receiving antenna 11, a propagation loss and a gain of the receiving antenna 11.
As a result, due to the transmission signal, the output signal of the band-pass filter 12 includes a frequency component (S_Txxe2x80x2) besides the frequency signal (S_Rx), and the output signal of the mixer 14 includes an intermediate frequency signal (IF_Rxxe2x80x2) besides the intermediate frequency signal (IF_Rx). Thus, a base noise is inevitably generated with the output of the of the active devices such as the low-noise amplifier and the frequency mixer 14 which are to receive the frequency component (S_Txxe2x80x2). Doubtlessly, the noise degrades the performance of the low-noise amplifier and the frequency mixer 14, resulting in degradation of performance of the receiving apparatus.
Therefore, an object of the present invention is to provide a transmitting/receiving apparatus of a repeater system which is capable of removing a frequency component generated in a receiving apparatus due to a transmission signal to thereby improve performance of a repeater system.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, there is provided a transmitting apparatus and a receiving apparatus of a repeater system in which a signal received by the receiving apparatus from a base station is amplified to a high-powered transmission signal by the transmitting apparatus so as to be transmitted to a destination, wherein the transmitting apparatus varies a phase and a magnitude of the transmission signal and applies a compensation signal to the receiving apparatus, and the receiving apparatus adds the inputted compensation signal and a signal inputted through a receiving antenna and removes an unnecessary frequency component caused due to interference of the transmission signal.
In order to achieve the above object, the receiving apparatus includes a receiving antenna for receiving a signal propagated from a base station; a band-pass filter for filtering the output of the receiving antenna; an adder for adding the output of the band-pass filter and a compensation signal; a low-noise amplifier for amplifying the output signal of the adder; and a first mixer for mixing a local signal with the output of the low-noise amplifier to convert it to an intermediate frequency signal.
In order to achieve the above object, the transmitting apparatus includes a second mixer for mixing the intermediate frequency signal outputted from the first mixer and a local signal to generate a radio frequency signal; a power amplifier for amplifying the radio frequency signal outputted from the second mixer; a low-pass filter for filtering the output signal of the power amplifier; a transmitting antenna for transmitting the output signal of the low-pass filter toward a destination; a phase converter for converting by xc2x1180xc2x0 a phase of the signal amplified by the power amplifier; and a variable amplifier for variably amplifying the output signal of the phase converter and generating a compensation signal.